Stability In Total Hip Arthroplasty Research Articles

Determination of a Safe Zone for Ischial Screw Placement in Total Hip Arthroplasty

BackgroundImplantation of acetabular components with supplemental screw fixation is commonly performed to improve osteointegration and long-term stability in total hip arthroplasty (THA). Placement of ischial screws improves stability in biomechanical studies, but can be technically challenging. The study aimed to provide a safe zone for ischial screw placement with reference to easily identifiable intra-operative landmarks. MethodsA retrospective review of patients was performed and 27 preoperative pelvis computed tomography scans were collected. After converting these images to 3-dimensional reconstructions of the pelvis, a safe zone for ischial screw placement was established with reference to the anterior superior iliac spine (ASIS) and the acetabular center and rim. ResultsThe safe zone of an ischial screw in the en face sagittal plane was a median of 17 degrees (interquartile range [IQR]: 11,23) anterior to 13 degrees (IQR: 10,18) posterior to the reference line from the ASIS through the center of the acetabulum. The safe zone in the coronal plane was 34 degrees (IQR: 18,68) medial to 13 degrees (IQR: 8,19) lateral from a start point 1 centimeter medial to the inferior acetabular rim with a screw length of 25 millimeters. An ischial screw optimized for length directed down the center of the ischium was qualitatively demonstrated to have a start point unobtainable intraoperatively, originating within the cotyloid fossa. ConclusionThe ASIS, center of the acetabulum, and acetabular rim provide identifiable intraoperative landmarks for guiding ischial screw placement in hip arthroplasty.

Comparison of the Mechanical and Osseointegrative Performance of Porous Tantalum and Titanium for Acetabular Implantation in Total Hip Arthroplasty: A Literature Review

Introduction: Stability of the acetabular component is a critical factor in the success of primary and revision total hip arthroplasty (THA) procedures. As such, the identification of implant surface characteristics that maximize stability of the acetabular cup is an important research objective. While titanium has historically been the most commonly used implant material, the proportion of THA procedures utilizing porous tantalum (PTa) implants has increased in recent years. The objective of this review is to examine the comparative mechanical and osseointegrative performance of PTa and porous titanium (PTi) and interpret these results in the context of primary and secondary stability of acetabular implants in THA, as characterized by strength of initial mechanical attachment and successful interlocking at the bone-implant interface, respectively. Methods: A literature search using a predetermined protocol and inclusion criteria yielded 7 articles presenting results of comparative testing of mechanical performance or osseointegration of PTa and PTi in the context of THA. Results: Neither PTa nor PTi presented consistently superior results in mechanical tests designed to correlate to primary stability at the metallo-biological surface nor in measures of osseointegration intended to represent secondary stability in THA. Discussion: In comparing PTa and PTi, it appears that the characteristics of the implant coating's pores may have a more significant impact on factors affecting the stability of an acetabular cup implant than the metal selected. However, determining the ideal pore morphology for this application is complex; pore characteristics that would suggest mechanical compatibility may conflict with those that would encourage more effective osseointegration. Conclusion: When extrapolated to be indicators of hypothetical clinical success, the results of this review are consistent with those of recently released macro-analyses of clinical outcomes: PTa and PTi acetabular cups, as they are currently manufactured, produce clinically equivalent outcomes. In the development and comparison of coating options, pore morphology and its complex effects on stability must be adequately accounted for; only then can we reach a faithful conclusion regarding the ideal porous adhesion surface for acetabular implant in THA.

Simulating movements of daily living in robot-assisted total hip arthroplasty with 3D modelling.

Computer-assisted 3D preoperative planning software has the potential to improve postoperative stability in total hip arthroplasty (THA). Commonly, preoperative protocols simulate two functional positions (standing and relaxed sitting) but do not consider other common positions that may increase postoperative impingement and possible dislocation. This study investigates the feasibility of simulating commonly encountered positions, and positions with an increased risk of impingement, to lower postoperative impingement risk in a CT-based 3D model. A robotic arm-assisted arthroplasty planning platform was used to investigate 11 patient positions. Data from 43 primary THAs were used for simulation. Sacral slope was retrieved from patient preoperative imaging, while angles of hip flexion/extension, hip external/internal rotation, and hip abduction/adduction for tested positions were derived from literature or estimated with a biomechanical model. The hip was placed in the described positions, and if impingement was detected by the software, inspection of the impingement type was performed. In flexion, an overall impingement rate of 2.3% was detected for flexed-seated, squatting, forward-bending, and criss-cross-sitting positions, and 4.7% for the ankle-over-knee position. In extension, most hips (60.5%) were found to impinge at or prior to 50° of external rotation (pivoting). Many of these impingement events were due to a prominent ischium. The mean maximum external rotation prior to impingement was 45.9° (15° to 80°) and 57.9° (20° to 90°) prior to prosthetic impingement. No impingement was found in standing, sitting, crossing ankles, seiza, and downward dog. This study demonstrated that positions of daily living tested in a CT-based 3D model show high rates of impingement. Simulating additional positions through 3D modelling is a low-cost method of potentially improving outcomes without compromising patient safety. By incorporating CT-based 3D modelling of positions of daily living into routine preoperative protocols for THA, there is the potential to lower the risk of postoperative impingement events.

Bibliometric Analysis of Spinopelvic Alignment in Total Hip Arthroplasty.

Postoperative dislocation of unclear etiology remains a concern after total hip arthroplasty (THA). Interest is growing in the importance of spinopelvic alignment on stability in THA. The purpose of this study was to analyze publication trends, areas of interest, and future research direction of spinopelvic alignment in THA. Articles on the topic of spinopelvic alignment in THA published between 1990 and 2022 were obtained through Web of Science Core Collection of Clarivate Analytics (WSCCA). Results were screened by title, abstract, and full text. The inclusion criterion was English-language peer-reviewed journal publications on the clinical topic of spinopelvic alignment in THA. Bibliometric software was used to characterize publication trends. We screened 1,211 articles, yielding 132 meeting the inclusion criterion. From 1990 to 2022, published articles have steadily increased, peaking in 2021. Countries that have been the most productive in contributions to research are those in which THA is the most prevalent. Our analysis of keyword frequency showed increasing interest in "pelvic tilt," "anteversion," and "acetabular component" position. Our study identified that increasing attention is being given to spinopelvic mobility and PT in the setting of THA. The United States and France produced the most studies related to spinopelvic alignment.

Current Evidence for Spinopelvic Characteristics Influencing Total Hip Arthroplasty Dislocation Risk.

Decreased pelvic mobility and pelvic retroversion may result from spinal degeneration and lead to changes in the orientation of the acetabular implant after total hip arthroplasty (THA). While multiple patient and surgery-related factors contribute to THA dislocations, there is increasing evidence that sagittal spinopelvic dynamics are relevant for THA stability. The aim of this systematic review was to assess the relationship between previously described sagittal spinopelvic characteristics and implant dislocations after primary THA. A comprehensive literature search in the PubMed and Embase databases was conducted for studies reporting on spinopelvic morphology, alignment, pathology, or surgery and THA dislocations. Risk of bias was assessed using the MINORS criteria. Because of high heterogeneity in study methodology, a synthesis of best evidence was performed. Odds ratios (ORs), relative risks (RRs), and effect sizes (g) were calculated. Fifteen studies (1,007,900 THAs) with quality scores of 15 to 23 out of 24 were included. Nine different spinopelvic alignment parameters (8 studies, g = 0.14 to 2.02), spinal pathology (2 studies, OR = 1.9 to 29.2), and previous spinal fusion surgery (8 studies, OR = 1.59 to 23.7, RR = 3.0) were found to be related to THA dislocation. Conflicting results were found for another sagittal pelvic morphology parameter, pelvic incidence. Several sagittal spinopelvic patient characteristics were found to be related to THA dislocation, and the associated risks were greater than for other patient and surgery-related factors. Future research is needed to determine which of those characteristics and parameters should be taken into account in patients undergoing primary THA. Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Effect of surface topography and residual stress on the taper connection stability in total hip arthroplasty

In the present work, the influence of the trunnion surface topography and the near-surface residual stresses on the joining process of a taper connection is examined using a replicate of the realistic taper connection as it occurs in conventional hip joint implants. The focus of the work is on the surface of the taper trunnion made of Ti6Al4V ELI and its effect on the connection stability with a CoCrMo counterpart. In this regard, the interrelation between surface topography, residual stresses, the joining behavior and the corrosion behavior under dynamic loading have been systematically investigated. For this purpose, taper trunnions produced by means of three different machining processes were considered, i.e. fine machining, rough machining and a novel furrowing process. These mechanical surface treatments result in different surface topographies and near-surface work hardening and residual stress states. The results show that the primary taper stability is hardly altered by the different types of trunnion surfaces. For all three surface states, the joining/dismantling procedure did not change the residual stress state at the surface. After corrosion testing under dynamic loading, the fine machined taper surface exhibits the highest stability. Moreover, fine machined tapers consolidated during the dynamic corrosion experiment as the ratio between joining and dismantling force increased from 0.49 ± 0.04 to 0.83 ± 0.08. For the furrowed and rough machined taper surfaces, the connection stability showed a tendency towards increase and decrease, respectively, in the course of dynamic corrosion testing. The results indicate that for choosing an optimal taper trunnion surface, the effects of corrosion must be taken into account.

Influence of acetabular cup thickness on seating and primary stability intotal hip arthroplasty.

Insufficient primary stability of acetabular hip cups is a complication resulting in early cup loosening. Available cup designs vary in terms of wall thickness, potentially affecting implant fixation. This study investigated the influence of different wall thicknesses on the implantation process and the resulting primary stability using excised human acetabula. Implantations were performed using a powered impaction device providing consistent energy with each stroke. Two different wall thicknesses were compared in terms of seating progress, polar gap remaining after implantation, bone-to-implant contact area, cup deflection, and lever out moment. Thin-walled cups showed higher lever out resistance (p < 0.001) and smaller polar gaps (p < 0.001) with larger bone contact towardthe dome of the cup (p < 0.001) compared to thick-walled cups. Small seating steps at the end of the impaction process were observed if a high number of strokes were needed to seat the cup (p = 0.045). A high number of strokes led to a strain release of the cup during the final strokes (p = 0.003). This strain release is indicative for over-impaction of the cup associated with bone damage and reduced primary stability. Adequate cup seating can be achieved with thin-walled cups with lower energy input in comparison to thicker ones. Thin-walled cups showed improved primary stability and enable implantation with lower energy input, reducing the risk of over-impaction and bone damage. Additional strokes should be avoided as soon as no further seating progress has been observed.

Radiological comparison of acetabular anteversion on cross-table lateral roentgenograms and computed tomograms functional outcomes in total hip arthroplasty

Introduction: Orientation and Alignment of prosthetic components are vitally important for the stability of total hip arthroplasty. Poor acetabular positioning is one of the many issues implicated with persistent pain due to impingement, dislocation, edge loading and liner fracture, which may be lead to patient dissatisfaction after total hip arthroplasty. Material and methods: Post-operative radiological analysis of the version of acetabulum through X-ray images and CT images was performed. Pre & post-operative scoring according to Modified Harris Hip Score (HHS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Oxford Hip Score (OHS) was documented. Results: A total of 55 patients were included in the study. The mean anteversion angle calculated on cross-table lateral radiograph by Woo and Morrey's method was 22.410 (Range 16-560), compared to CT Scans measured was 28.640 (Range 11.10-50.100). Conclusion: Majority 69.09 % of patients had excellent functional outcomes in a range of 11.1-360 of anteversion compared to Lewinnek’s safe zone. It suggests that there is flexibility in positioning the acetabular component than previously believed. If one has to err, it should be towards more anteversion. Infact to avoid dislocation, more anteversion is required to guard against unwarranted activities on part of the patient.

Radiological comparison of acetabular anteversion on roentgenograms and computed tomograms functional outcomes in total hip arthroplasty

Introduction: Orientation and Alignment of prosthetic components are vitally important for the stability of total hip arthroplasty. Poor acetabular positioning is one of the many issues implicated with persistent pain due to impingement, dislocation, edge loading and liner fracture, which may be lead to patient dissatisfaction after total hip arthroplasty. Material and methods: Post-operative radiological analysis of the version of acetabulum through X-ray images and CT images was performed. Pre & post-operative scoring according to Modified Harris Hip Score (HHS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Oxford Hip Score (OHS) was documented. Results: A total of 55 patients were included in the study. The mean anteversion angle calculated on anteroposterior (AP) radiographs by Lewinnek’s method was 23.480 (Range 11 – 390) and on cross-table lateral radiograph by Woo and Morrey's method was 22.410 (Range16 – 560), compared to CT Scans measured was 28.640 (Range 11.10 – 50.100). Conclusion: Majority 69.09% of patients had excellent functional outcomes in a range of 11.1 – 360 of anteversion compared to Lewinnek’s safe zone. It suggests that there is flexibility in positioning the acetabular component than previously believed. If one has to err, it should be towards more anteversion. Infact to avoid dislocation, more anteversion is required to guard against unwarranted activities on part of the patient.

Radiological comparison of acetabular anteversion on anteroposterior roentgenograms and computed tomograms functional outcomes in total hip arthroplasty

Introduction: Orientation and Alignment of prosthetic components are vitally important for the stability of total hip arthroplasty. Poor acetabular positioning is one of the many issues implicated with persistent pain due to impingement, dislocation, edge loading and liner fracture, which may be lead to patient dissatisfaction after total hip arthroplasty. Material and methods: Post-operative radiological analysis of the version of acetabulum through X-ray images and CT images was performed. Pre & post-operative scoring according to Modified Harris Hip Score (HHS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Oxford Hip Score (OHS) was documented. Results: A total of 55 patients were included in the study. The mean anteversion angle calculated on anteroposterior (AP) radiographs by Lewinnek’s method was 23.480 (Range 11 – 390), compared to CT Scans measured was 28.640 (Range 11.10 – 50.100). Conclusion: Majority 69.09% of patients had excellent functional outcomes in a range of 11.1 – 360 of anteversion compared to Lewinnek’s safe zone. It suggests that there is flexibility in positioning the acetabular component than previously believed. If one has to err, it should be towards more anteversion. Infact to avoid dislocation, more anteversion is required to guard against unwarranted activities on part of the patient.

Targeting the safe zones for cup position without fluoroscopic guidance in total hip arthroplasty: does the surgical approach affect the outcomes?

Proper acetabular cup positioning is crucial for achieving implant longevity and stability in total hip arthroplasty (THA). One of the elements that may affect the accuracy and precision of the positioning of the cup is the type of surgical approach used. This study compares the accuracy and the precision of conventional free-hand acetabular cup positioning relative to different "safe zones" in two groups of patients operated with THA using two different surgical approach. Retrospective radiological comparative matched-pair controlled study of two groups of patients operated with primary THA: the first group was operated in supine decubitus with a mini-invasive direct anterior approach (DA group), the second group was operated in lateral decubitus with a conventional posterolateral approach (PL group). Cup inclination and anteversion were assessed using the digital planning software TraumaCad. Cup position in the two groups were compared in terms of accuracy and precision. Forty four patients were enrolled for each group. The DA group showed a less inclined and less anteverted cup compared to the PL group (respectively 38.5 ± 5.2 vs. 49.6 ± 5.6 and 16.2 ± 3.6 vs. 22.9 ± 6.4; p < 0.01). The DA group showed a significantly higher percentage of cups within the "safe zone" in 4 out of 6 reference zones and a significantly lower variance in anteversion (12.96 vs. 40.96, p < .01). There was no difference in the variance for inclination. Our study found greater accuracy and precision in the positioning of the cup when surgery was performed through a direct anterior approach compared to the posterolateral approach due to the supine position of the patient which allows greater stability of the pelvis during surgery and makes it easier to target the desired angular references for cup positioning.

Intraprosthetic dislocation after a revision hip replacement: a case report

ABSTRACT BACKGROUND: The dual mobility cup (DMC) was initially design in 1974. It was designed to offer additional stability in total hip arthroplasty (THA) and to prevent dislocations. The dissociation of a DMC has been termed an intraprosthetic dislocation (IPD) and is a rare complication. It is defined as separation of the articulation between the polyethylene and head articulation in the DMC. As the utilisation of DMCs in orthopaedic surgery increases, we can expect an increase in this rare complication. We report a case of an IPD in the setting of revision hip arthroplasty in a 72-year-old female. CASE REPORT: The report is on a 72-year-old female patient who underwent revision hip arthroplasty. The articulation utilised was of the dual mobility type. Some eight months later she dislocated her hip. An attempted closed reduction under general anaesthesia with muscle relaxant was unsuccessful. Thereafter she was taken to surgery to perform an open reduction of the hip. Intra-operatively it was found that the dual mobility head had dissociated, with the polyethylene component remaining in the metal liner. A revision of the components was performed. DISCUSSION: We postulate on the mechanisms of dissociation of the dual mobility head. We review the current literature related to IPD and discuss the risk factors associated with this rare complication. CONCLUSION: The diagnosis of IPD is an indication for revision surgery of the DMC. When utilising a DMC, care should be taken to mitigate against the known risk factors for IPD. All dual mobility dislocations should be reduced under general anaesthesia with muscle relaxant Level of evidence: Level 4.. Keywords: intraprosthetic dislocation, dual mobility cup, revision hip arthroplasty

The Direct Anterior Approach Total Hip Arthroplasty Reliably Achieves "Safe Zones" for Combined Anteversion.

BackgroundIn total hip arthroplasty (THA), component position is critical to avoid instability and improve longevity. Appropriate combined femoral and acetabular component anteversion is important for improved THA stability and increased impingement-free range of motion. In direct anterior THA (DA-THA), concern has been expressed regarding the accuracy of femoral component positioning. This study seeks to quantify acetabular, femoral, and combined component orientation relative to the accepted “safe zones” in patients who have undergone DA-THA.MethodsTwenty-nine patients who had THA performed via direct anterior approach had postoperative computerized tomography scans done to assess femoral anteversion. Stem rotational alignment was measured relative to the transepicondylar axis (TEA) and the posterior condylar axis (PCA) of the femur at the knee. Acetabular abduction and version were recorded on anteroposterior pelvis radiographs.ResultsThe mean stem anteversion was 17.5° (standard deviation = 10.8°) from the TEA and 21.7° (standard deviation = 11.3°) from the PCA. Ten of 30 cups were appropriately anteverted; however, all the cups had appropriate abduction. Combined version when using the TEA resulted in 79% (23/29) of patients within the “safe zone” of 25°-50°. Pearson correlation coefficients were high for both stem anteversion from the TEA (R = 0.96) and PCA (R = 0.98); however, interobserver reliability for combined component anteversion was greater for the TEA (kappa, 0.83 vs 0.65).ConclusionsCombined anteversion within the “safe zone” was achieved 79% of the time with DA-THA. Interestingly, most of the “excessive” combined anteversion appears to be related to increased anteversion of the acetabular component with only 10 patients within the acetabular cup “safe zone” of 5°-25°.

Obesity Alters Spinopelvic Alignment Changes From Standing to Relaxed Sitting: the Influence of the Soft-tissue Envelope.

BackgroundChanges in spinopelvic and lower extremity alignment between standing and relaxed sitting have important clinical implications with regard to stability of total hip arthroplasty. This study aimed to analyze the effect of body mass index (BMI) on lumbopelvic alignment and motion at the hip joint.MethodsA retrospective review of patients who underwent full-body stereoradiographs in standing and relaxed sitting for total hip arthroplasty planning was conducted. Spinopelvic parameters measured included spinopelvic tilt (SPT), pelvic incidence (PI), lumbar lordosis (LL), PI minus LL (PI-LL), proximal femoral shaft angle (PFSA), and standing-to-sitting hip range of motion. Propensity score matching controlled for age, gender, PI, and hip ostoarthritis grade. Patients were stratified into normal (NORMAL; BMI, 18.5-24.9), overweight (OW; 25.0-29.9), and obese (OB; 30.0-34.9) groups. Alignment parameters were compared using one-way analysis of variance.ResultsThere were 84 patients in each group after propensity score matching. Standing alignment between BMI groups was similar for all parameters (P > .05) except for PFSA (P < .001). Significant differences were noted for sitting alignment between patients who are NORMAL, OW, and OB in: SPT (P = .007), PI-LL (P = .018), and LL (P = .029). PFSA between groups was not significantly different (P > .05). Significant differences were found for sitting-to-standing alignment across groups in PFSA change (P < .001), SPT change (P = .006), PI-LL change (P = .005), LL change (P = .037), and hip flexion (P < .001).ConclusionsSignificant differences in sitting and standing-to-sitting change in lumbopelvic alignment based on BMI suggest obese patients recruit more posterior spinopelvic tilt when sitting to compensate for soft-tissue impingement that occurs anterior to the hip joint and limiting hip flexion.

Is there a reduction in risk of revision when 36-mm heads instead of 32 mm are used in total hip arthroplasty for patients with proximal femur fractures?

Background and purpose — 32-mm heads are widely used in total hip arthroplasty (THA) in Scandinavia, while the proportion of 36-mm heads is increasing as they are expected to increase THA stability. We investigated whether the use of 36-mm heads in THA after proximal femur fracture (PFF) is associated with a lower risk of revision compared with 32-mm heads.Patients and methods — We included 5,030 patients operated with THA due to PFF with 32- or 36-mm heads from the Nordic Arthroplasty Register Association database. Each patient with a 36-mm head was matched with a patient with a 32-mm head, using propensity score. The patients were operated between 2006 and 2016, with a metal or ceramic head on a polyethylene bearing. Cox proportional hazards models were fitted to estimate the unadjusted and adjusted hazard ratio (HR) with 95% confidence intervals (CI) for revision for any reason and revision due to dislocation for 36-mm heads compared with 32-mm heads.Results — 36-mm heads had an HR of 0.9 (CI 0.7–1.2) for revision for any reason and 0.8 (CI 0.5–1.3) for revision due to dislocation compared with 32-mm heads at a median follow-up of 2.5 years (interquartile range 1–4.4).Interpretation — We were not able to demonstrate any clinically relevant reduction of the risk of THA revision for any reason or due to dislocation when 36-mm heads were used versus 32-mm. Residual confounding due to lack of data on patient comorbidities and body mass index could bias our results.

Relationship between use of screws and acetabular cup stability in total hip arthroplasty: a meta-analysis.

ObjectiveThe relationship between the use of screws and acetabular cup stability in total hip arthroplasty (THA) remains controversial. We evaluated cup stability in THA with and without the use of screws.MethodsWe performed a systematic literature search to identify studies on cup stability relative to the use of screws in patients undergoing THA before October 2018. Methodological quality assessment and data collection were performed by two individual reviewers. Meta-analysis was performed using Review Manager version 5.3.5.ResultsWe included seven trials involving 1402 patients (1469 THAs): 767 patients (809 THAs) with screws and 635 patients (660 THAs) without screws. The findings of meta-analysis indicated that uncemented acetabular component fixation with the use of additional screws was not correlated with migration of the cup, migration on roentgen stereophotogrammetry, or reoperation after THA. Moreover, operation time was not significantly different according to whether screws were used. There was no relationship between use of additional screws and osteoporosis or Harris Hip Score; however, THA with or without the use of screws might be related to bone sclerosis in the C1 region.ConclusionCurrently, limited evidence shows that the use of screws during THA may not improve cup stability.

Prospective Evaluation of the Posterior Tissue Envelope and Anterior Capsule After Anterior Total Hip Arthroplasty

BackgroundFemoral exposure for direct anterior approach (DAA) total hip arthroplasty (THA) invariably requires posterior soft tissue releases. Released posterior structures cannot be repaired. The purpose of this study is to describe the frequency and anatomic consequences of DAA THA posterior soft tissue releases and to compare the appearance of the anterior capsule between a group of patients who had capsulotomy and repair versus capsulectomy. MethodsThirty-two DAA THA patients underwent metal artifact reduction sequence magnetic resonance imaging at discharge and 1-year follow-up. Seventeen had underwent capsulotomy and repair and 15 capsulectomy. A radiologist blinded to intraoperative data scored each metal artifact reduction sequence magnetic resonance imaging. Anterior capsular integrity, status of the piriformis and conjoint tendons, and muscle atrophy were graded. Descriptive statistics were performed to analyze results. ResultsImmediately postoperatively, 75% of piriformis tendons were intact and 38% of conjoined tendons were intact. At 1 year, 97% had an intact piriformis and conjoined tendon, although many were in continuity through scar with the capsule. The posterior capsule directly contacted bone in all patients. At 1 year, none of the patients who underwent capsulotomy with repair had persistent anterior capsule defects, while 27% in the capsulectomy group had persistent defects. ConclusionPosterior capsule and conjoined tendon releases were commonly performed during DAA THA, yet continuity with bone was frequently achieved at 1 year. In this study, capsulotomy with repair resulted in no anterior capsular defects when compared with capsulectomy. These results may support improved THA stability observed after DAA with capsular repair despite posterior soft tissue releases. Level of EvidenceLevel III, prospective cohort study.

A Geometric Model to Determine Patient-Specific Cup Anteversion Based on Pelvic Motion in Total Hip Arthroplasty.

Introduction Cup position is critical to stability in total hip arthroplasty and is affected by pelvis motion during positions of daily life. The purpose of this study was to explicitly define the relationship between sagittal pelvic motion and resultant cup functional anteversion and create a tool to guide the surgeon to a patient-specific intra-operative anteversion. Materials and Methods 10,560 combinations of inclination, anteversion, and pelvic tilt were generated using a geometric model. Resultant functional anteversion was calculated for each iteration and variables were correlated. An electronic mobile tool was created that compares inputted patient-specific values to population-based averages to determine pelvic positions and dynamics that may lead to instability. Results A third-degree polynomial equation was used to describe the relationship between variables. The freely downloadable mobile tool uses input from pre-operative plain radiographic measurements to provide the surgeon a quantitative correction to intra-operative cup anteversion based on differences in functional anteversion compared to population-based averages. Conclusion This study provides a geometric relationship between planned cup position, pelvic position and motion, and the resultant functional anteversion. This mathematical model was applied to an electronic tool that seeks to determine an individualized intra-operative cup anteversion based on measured patient-specific pelvic dynamics.

Influence de la position du centre de la hanche, de la morphologie de l’épine iliaque antéro-inférieure et du diamètre de la tête prothétique sur la mobilité articulaire après arthrosplastie totale

BackgroundAcetabular component orientation, such as high placement and femoral head diameter influence joint stability in total hip arthroplasty (THA), wherein anterior inferior iliac spine (AIIS) shape could cause femoro-acetabular impingement. Little is known regarding the combined influence of these parameters, particularly in the context of developmental dysplasia of the hip. Therefore we conducted a computer simulation study based on computed tomography (CT) data to determine whether: (1) AIIS shape, (2) high placement of acetabular cups, and (3) ball head diameter influence the range of motion (ROM) after THA. HypothesisThe decrease in ROM depends on AIIS shape and the ROM decreases even if the femoral head diameter is increased when high placement of acetabular cups. Patients and methodsCT data from 14 hips of 14 patients were evaluated. Hips were categorized by Hetsroni classification type I (n=6), type II (n=6), and type III (n=2) depending on AIIS shape. ROM was evaluated using CT-based software. Cups were placed at and 5 and 10mm above the normal hip position. The femoral heads used were 28 (standard simulation), 32, and 36mm in diameter. ROM at impingement was measured under flexion (Flex), internal rotation (IR) at 90° flexion (IR at 90Flex), IR at 45° flexion with a 20° adduction (IR at 45Flex20Add), and external rotation at 10° extension (ER at 10Ext). ResultsThe mean ROM standard simulation for Flex, IR at 90Flex, IR at 45Flex20Add and ER at 10Ext were: 119.8±5.4°, 31.0±11.3°, 70.0±11.9°, and 33.0±9.7° for type I; 118.5±5.5°, 31.5±2.9°, 71.3±2.2°, and 33.3±3.3° for type II; and 105.5±13.4°, 21.0±15.6°, 61.0±11.3°, and 34.5±2.1° for type III, respectively. There were no significant differences in the ROMs of each type (Flex, p=0.252; IR at 90Flex, p=0.461; IR at 45Flex20Add, p=0.261; and ER at 10Ext, p=0.655). For the high placement of acetabular cups, ROM increase was restricted despite the femoral head diameter increase. DiscussionLarger femoral head diameters increased ROM, with a lower increase in type III because of bony impingement. ROM decreased with higher cup placement. Expansion effects were minimal, even with larger ball head diameters, and were further decreased in types II and III. Attention should be paid to AIIS shape because bony impingements occur early with higher acetabular cup placement. Level of evidenceVI, Simulation study.

Enhanced stability in total hip arthroplasty

For some patients, total hip arthroplasty (THA) continues to be complicated by postoperative instability and dislocation. The risk of dislocation is markedly higher in patients with predisposing conditions, including coexisting spinal pathology. In these patients, implant design and choice may offer added stability. Larger femoral heads, dual mobility constructs, constrained acetabular liners, and elevated acetabular liners offer enhanced stability in patients who are at risk for postoperative instability. Similarly, pre-operative templating, surgical approach, and surgical techniques such as trochanteric advancement may also influence stability. This review will discuss the evidence, advantages, and disadvantages of the various implant options and surgical techniques for enhancing stability in high risk patients after THA.